As digital image photographing apparatuses, such as digital still cameras and mobile phones having a camera function, gain popularity, hard discs and other recording media for recording photographed images have become available inexpensively.
Generally, users of digital image photographing apparatuses and the like (hereinafter simply referred to as users) store photographed images on a recording medium such as a hard disc with a large capacity.
If the number of stored images grows large, users have difficulty searching for a particular image. To facilitate searching, images may be classified into categories.
An example of technology for classifying images is to extract features of an image and use the extracted features to classify the image, as described in Patent Literature 1 and Patent Literature 2. Another known form of technology is to classify images based on the image capture time, as described in Patent Literature 3.